diff3

Show differences among three files.
When two people have made independent changes to a common original, `diff3' can report the differences between the original and the two changed versions, and can produce a merged file that contains both persons' changes together with
warnings about conflicts.
The files to compare are mine, older, and yours. At most one of these three file names can be -, which tells diff3 to read the standard input for that file.

Syntax
diff3 [options] mine older yours
Options
-a Treat all files as text and compare them line-by-line,
even if they do not appear to be text.
-A Incorporate all changes from older to yours into mine,
surrounding all conflicts with bracket lines.
-e Generate an ed script that incorporates all the
changes from older to yours into mine.
-E Like -e, except bracket lines from overlapping
changes' first and third files. With -e, an over-
lapping change looks like this:
<<<<<<< mine
lines from mine
=======
lines from yours
>>>>>>> yours
--ed Generate an ed script that incorporates all the
changes from older to yours into mine.
--easy-only
Like -e, except output only the nonoverlapping changes.
-i Generate w and q commands at the end of the ed
script for System V compatibility. This option
must be combined with one of the -AeExX3 options,
and can not be combined with -m.
--initial-tab
Output a tab rather than two spaces before the text
of a line in normal format. This causes the alignment
of tabs in the line to look normal.
-L label
--label=label
Use the label label for the brackets output by the
-A, -E and -X options. This option can be given up
to three times, one for each input file. The
default labels are the names of the input files.
Thus diff3 -L X -L Y -L Z -m A B C acts like diff3
-m A B C , except that the output looks like it
came from files named X, Y and Z rather than from
files named A, B and C.
-m
--merge
Apply the edit script to the first file and send
the result to standard output. Unlike piping the
output from diff3 to ed, this works even for binary
files and incomplete lines. -A is assumed if no
edit script option is specified.
--overlap-only
Like -e, except output only the overlapping changes.
--show-all
Incorporate all unmerged changes from older to
yours into mine, surrounding all overlapping
changes with bracket lines.
--show-overlap
Like -e, except bracket lines from overlapping
changes' first and third files.
-T Output a tab rather than two spaces before the text
of a line in normal format. This causes the align-
ment of tabs in the line to look normal.
--text Treat all files as text and compare them line-by-
line, even if they do not appear to be text.
-v
--version
Output the version number of diff3.
-x Like -e, except output only the overlapping
changes.
-X Like -E, except output only the overlapping changes.
In other words, like -x, except bracket changes as in -E.
-3 Like -e, except output only the nonoverlapping
changes.

NotesMultiple single letter options (unless they take an argument) can be combined into a single command line argument.

`diff3' normally compares three input files line by line, finds groups of lines that differ, and reports each group of differing lines. Its output is designed to make it easy to inspect two different sets of changes
to the same file.

An exit status of 0 means diff3 was successful, 1 means some conflicts were found, and 2 means trouble.

“One person can make a difference and every person must try” ~ John F. Kennedy